Contacting device

ABSTRACT

The present invention relates to a device for contacting a wafer during submersion in a liquid. The device comprises a main body fixed to a transportation device; an electrical contact for contacting the wafer and a pressure element for pressing the electrical contact towards the wafer.

FIELD OF THE INVENTION

The present invention relates to a device for contacting a solar cellwafer.

BACKGROUND OF THE INVENTION

In UK patent application 0709619.1 it is described a device for exposinga solar cell wafer to a liquid, comprising a container filled with theliquid; a transportation device for transporting the wafer through theliquid; and a carrier device for carrying the wafer together with thetransportation device.

In UK patent application 0719805.4 it is shown a device for supplyingelectrical power to a wafer that is at least partially submerged in aliquid, comprising a liquid container filled with the liquid; atransportation device comprising a wafer carrier device for transportingthe wafer at least partially submerged through the liquid; and a powersupply device for supplying electrical power to the wafer.

These publications are for example used in electroplating processeswhere for example Ni, Cu, Sn and/or Ag is applied to the wafer.

A challenge in this process is to provide electrical contact to thewafer without applying strong mechanical forces to the wafer, which maycause breakage of the wafer. Moreover, it is a need to improve the speedof the process for large scale production of solar cells. Inelectroplating, this is done by increasing the current density appliedto the wafer since the number of metal atoms deposited on the wafersurface is directly proportional to the current applied to the wafer.However, there is an upper limit for the current density called thelimiting diffusion current density I_(L) (I_(L)=(nFD_(ox)c_(b))/δ).(ref. page 97 M. Paunovic and M. Schlesinger, Fundamentals ofElectrochemical Deposition Second Ed., pp. 97, John Wiley and Sons,2006). I_(L) is the value of the current where mass transport of ions tothe electrode/solution interface start to become the limiting factor forthe overall rate of reaction. By increasing the agitation at thesolution/electrode interface, the Nernst diffusion layer, δ, becomessmaller. In turn, this implies that I_(L) increases and the theoreticaldeposition rate of metal can be increased.

The object of the present invention is to improve the electrical contactto the wafer so the above conditions can be met. In particular, thedevice enables turbulent agitation from the same side as the contactsare applied to the wafer, while at the same time wafers continuously aremoving forward through the process.

SUMMARY OF THE INVENTION

The present invention relates to a device for contacting a wafer duringsubmersion in a liquid, comprising:

-   -   a main body fixed to a transportation device;    -   an electrical contact for contacting the wafer;    -   a pressure element for pressing the electrical contact and the        wafer towards the wafer.

In an aspect of the invention, the electrical contact is provided on thepressure element.

In an aspect of the invention, the pressure element is movably connectedto the main body.

In an aspect of the invention, the pressure element comprises a floatingelement.

In an aspect of the invention, the main body comprises a groove adaptedto receive an end of the wafer.

In an aspect of the invention, the electrical contact comprises anupwardly protruding contact.

In an aspect of the invention, the upwardly protruding contact isconnected to a bus connector for connection to a bus bar.

In an aspect of the invention, the upwardly protruding contact isconnected to the bus connector by means of an electric wire.

In an aspect of the invention, the device comprises severalindependently movable pressure elements having independent floatingelements.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described in detailwith reference to the enclosed drawings, where:

FIG. 1 shows a perspective view of three holding devices holding twowafers;

FIG. 2 shows a side view of FIG. 1;

FIG. 3 shows an enlarged side view of one of the holding devices in FIG.2;

FIG. 4 shows a perspective view from below of one of the holding devicein FIG. 4;

FIG. 5 shows a side view of the holding device in FIG. 2, where someparts are omitted;

FIG. 6 shows a perspective view of the holding device in FIG. 5;

FIG. 7 a shows a perspective view of a second embodiment of the holdingdevice;

FIG. 7 b shows a side view of the second embodiment;

FIG. 7 c shows the floating element of the second embodiment;

FIG. 7 d shows a front view of the second embodiment;

FIG. 8 a shows a perspective view of a third embodiment of a holdingdevice and bus bar;

FIG. 8 b shows a side view of the holding device and bus bar in FIG. 8a;

FIG. 8 c shows a front view of the holding device and bus bar in FIG. 8a;

FIG. 8 d shows a perspective view of the third embodiment, where themain body is removed;

FIG. 8 e shows a front view of the main body;

FIG. 9 shows a semi-transparent perspective view of a fourth embodiment;

FIG. 10 a shows a semi-transparent perspective view of a fifthembodiment;

FIG. 10 b shows a side view of the fifth embodiment of FIG. 10 a.

It is now referred to FIGS. 1 and 2, where three holding devices 10 a,10 b and 10 c are shown. The holding devices are mounted on atransportation device (not shown), for example such as those describedin the above-mentioned publications. One solar cell wafer 1 a is heldbetween the holding devices 10 a and 10 b, and one solar cell wafer 1 bis held between the holding devices 10 b and 10 c. Hence, the holdingdevices are provided for holding one end of a wafer on both sides. Theloading and unloading of wafers to the holding devices is also describedin the above-mentioned publications.

It should be noted the above-mentioned publications describe that theholding devices 10 are fixed to a continuous transportation device,where wafers are continuously received between two holding devices at afirst end of the transportation device, while other wafers arecontinuously released from the transportation device at a second end ofthe transportation device. During the transportation from the first endto the second end, the wafers are exposed to a process such assubmersion into a liquid, electroplating, etc. The first holding deviceis receiving and holding the front end of the wafer, while the secondholding device is receiving and holding the rear end of the wafer, wherethe terms “front” and “rear” is referring to the transportationdirection. Hence, each wafer is held between two holding devices 10.

It is now referred to FIGS. 3 and 4, showing a holding device 10corresponding to one of the holding devices 10 a, 10 b, 10 c.

The holding device 10 comprises a main body 12 with a substantiallywedge-shaped opening 14 a and 14 b on respective side. The substantiallywedge-shaped openings 14 a and 14 b are adapted to receive an end of awafer 1, as shown in FIG. 2. Grooves 16 are provided in the lower partof the main body 12 for fastening of the holding device 10 to thetransportation device.

The main body 12 comprises a longitudinal opening 18 defining a rotationaxis I-I as shown in FIG. 4. The opening 18 is provided in the lowerpart of the main body 12.

Pressure elements 20 are movably or pivotally connected in groovesprovided in the main body 12 to the opening 18, so that they can bepivoted around the rotation axis I-I. In FIG. 4 it is shown that threepairs of pressure elements 20 a and 20 b are provided in the lower partof the main body 12, where pressure elements 20 a are provided on theleft side and pressure elements 20 b are provided on the right side. Thepivotal connection of the pressure elements 20 can for example beprovided by a cylindrical pin 18 a being inserted through the opening 18of the main body 12 and corresponding openings in the pressure elements20 (see FIG. 6). As shown here, the pin 18 a is common for both pressureelements 20 a and 20 b.

The pressure elements 20 comprise floating elements 30 made of amaterial with a material with positive buoyancy. In the drawings, thefloating elements 30 are provided as separate cylindrical floatingelements 30 provided in peripherical openings (i.e. provided in adistance away from the pin 18 a). The floating elements 30 are hollowcylinders which will be sealed at the ends and therefore they containair for maximum positive buoyancy. The structures 20 a and 20 b arepreferably made of a material with positive buoyancy relative to theplating liquid (e.g. polypropylene). Both the size of 30 can be alteredand/or the distance of 30 to the axis 18 can be changed to reach thedesired force from the contacts to the wafer. Alternatively, thefloating elements 20 can be provided as a common floating element forall pressure elements 20 a and one common floating element for allpressure elements 20 b. Alternatively, the floating elements could beincorporated as a part of the pressure element 20 (i.e. the pressureelement made of a material with positive buoyancy).

An upwardly protruding electrical contact 40 is provided on eachpressure element 20 for contacting the wafer. In FIG. 3 it is seen thatwhen the pressure element 20 is pivoted upwards (in the direction ofarrow A), by means of the positive buoyancy caused by the floatingelement 30 when submerged in a liquid, the upwardly protrudingelectrical contact 40 will be pressing the wafer towards the uppersurface of the substantially wedge-shaped opening 14.

Hence, when the pressure element is in this upper or closed position,the holding device is both holding the wafer and at the same timeproviding electrical contact to the wafer. When the pressure element isin its lower or open position, the wafer may be received into orreleased from the holding device.

The upwardly protruding electrical contact 40 is connected to a plate 42made of a current conducting material. The plate 42 is fixed to thepressure element 20.

A bus connector 44 is provided on top of the main body 12. The busconnector 44 is in electrical contact with the plate 42 and theelectrical contact 40 by means of an electric wire 46 provided inchannels (not shown) in the main body 12. The electric wire 46 isflexible to allow the movement of the pressure element 20. The busconnector 44 is adapted to be in electrical contact with a bus bar (notshown) connected to a power supply. The bus connector 44 is shaped as alying U or V, to allow for unobstructed sliding along the bus bar.

In FIGS. 5 and 6 it is shown that the bus connector 44 is connected tothe electric contacts 40 of both the right pressure element 20 a and theleft pressure element 20 b. It would of course also be possible to haveone common bus connector for all six pressure elements.

It would of course be possible to provide electrical contact by usingmore than three contacts 40 for each side surface of the wafer and/or toadjust the distance between them.

It would also be possible to replace the three individual electricalcontacts 40 for one side of the wafer with one continuous electricalcontact.

SECOND EMBODIMENT

In FIG. 7 a-7 d a second embodiment of the holding device is shown. Thisholding device is denoted with reference number 110. Many detailsregarding the second embodiment will not be described in detail here, asthey are similar to those described above.

As described in detail with reference to the first embodiment, thedevice 110 comprises a main body 112 with a substantially wedge-shapedopening 114 a and 114 b on respective side.

The main body 112 comprises a longitudinal opening 118 provided in thelower part of the main body 112. A pressure element 120 is provided inthe opening 118 and allows the pressure element 120 to move upwardly ina substantially linear movement in the direction of arrow B. Thepressure element 120 is made of a floating material, i.e. has positivebuoyancy in the liquid being used. Alternatively, the pressure element120 comprises floating elements (not shown) for example incorporated inthe body of the pressure element. Ideally, the pressure element 120incorporates floating elements and the material in 120 is made of amaterial with a positive buoyancy relative to the liquid being used.

It is now referred to FIG. 7 c, where it is shown that the pressureelement 120 is substantially T-shaped (an inverted T, i.e. a T turnedupside down), comprising a substantially vertical central member 150 anda substantially horizontal cross member 152.

As can be seen in FIGS. 7 b and 7 c, the floating element 120 comprisesan upwardly protruding, substantially T-shaped element 121. The T-shapedelement 121 limits both the upwardly and downwardly movement of thepressure element 120 in the opening 118. The substantially T-shapedelement 121 corresponds to the substantially vertical central member 150of the pressure element 120.

Upwardly protruding electrical contacts 140 are provided on thesubstantially horizontal cross member 152 of the pressure element 120for contacting the wafer. These are in electrical contact with a busconnector (not shown), as described with reference to the abovementionedembodiment. The substantially horizontal cross member 152 is providedfor pressing each wafer towards the upper surface of the substantiallywedge-shaped opening 114 a, 114 b in a direction parallel to thesubstantially vertical central member 150.

When the pressure element 120 is submerged in liquid, its positivebuoyancy causes the pressure element to move upwards in the direction ofarrow B, and hence the electrical contacts 140 will contact the wafersprovided in the substantially wedge-shaped openings 114 a and 114 b.

Hence, when the pressure element is in this upper or closed position,the holding device is both holding the wafer and at the same timeproviding electrical contact to the wafer. When the pressure element isin its lower or open position, the wafer may be received into orreleased from the holding device.

THIRD EMBODIMENT

In FIG. 8 a-8 d a third embodiment of the holding device is shown. Thisholding device is denoted with reference number 210. Many detailsregarding the third embodiment will not be described in detail here, asthey are similar to those described above.

As described in detail with reference to the first embodiment, thedevice 210 comprises a main body 212 with a substantially wedge-shapedopening 214 a and 214 b on respective side.

A recess or opening 218 provided in the lower part of the main body 212(see FIG. 8 e). A pressure element 220 is provided in the opening 218.Three substantially cylindrical channels 219 are provided in the mainbody 212, as indicated with dashed lines in FIG. 8 c. Threesubstantially cylindrical poles 222 are provided in respective channels219. In their lower end, the poles 222 are fixed to the pressure element220. In their upper end, the poles 222 are provided with bus connectorsor knobs 244 made of an electrical conducting material. The knobs 244have a substantially spherical shape, and are having a larger diameterthan the poles 222. As seen in FIGS. 8 b and 8 c, the poles 222 arelonger than the channels 219.

Consequently, the pressure element 220 together with the poles 222 andknobs 244 are allowed to be moved upwardly and downwardly in asubstantially linear movement in the direction of arrow C. The movementis limited by the knobs 244 being larger than the channels 219 and bythe pressure element 222 meeting the lower part of the main body 212.

Upwardly protruding electrical contacts 240 are provided on the pressureelement 220 for contacting the wafer. These are in electrical contactwith the knobs 244. In this embodiment, bus bars 248 comprise pairs oftwo spaced apart bars, where the distance between each bar allows thepole 222 to pass through between. Moreover, the bus bars 248 are havingan inclining end 249.

Also in this embodiment, the pressure element may be considered as beingsubstantially T-shaped, comprising a substantially vertical centralmember 250 and a substantially horizontal cross member 252 (see FIG. 8d). Here, the substantially vertical central member 250 corresponds tothe poles 222. The substantially horizontal cross member 252 correspondsto the pressure element where the contacts 240 are fixed.

Also here, the substantially horizontal cross member 252 is provided forpressing each wafer towards the upper surface of the substantiallywedge-shaped opening 214 a, 214 b in a direction parallel to thesubstantially vertical central member.

Hence, when the pressure element is in this upper or closed position,the holding device is both holding the wafer and at the same timeproviding electrical contact to the wafer. When the pressure element isin its lower or open position, the wafer may be received into orreleased from the holding device. In the third embodiment, it is notbuoyancy that provides movement of the pressure element 220. Initially,the pressure element 220 is in its lower position. When approaching theend 249 of the bus bars 248, the poles 222 will pass between the bars,while the knobs 244 will be guided or pressed upwards because of theinclining end 249. Consequently, the poles and the pressure element willbe guided upwardly in the direction of arrow C, and the electricalcontacts 240 will contact the surface of the wafer. Of course, the busbars 248 will be located in a suitable position over the liquid.

The pressure element 220, poles 222 and knobs 244 may be provided with aspring mechanism (not shown) to dampen the pressure and movement of thepressure element. Alternatively, the poles 222 could be made of aflexible material, or the bus bars could be provided with a springmechanism.

The abovementioned detailed description is especially provided toillustrate and to describe preferred embodiments of the invention.However, the description is by no means limiting the invention to thespecific embodiments.

FOURTH EMBODIMENT

In FIG. 9 a fourth embodiment of the holding device is shown. Thisholding device is denoted with reference number 310. Many detailsregarding the third embodiment will not be described in detail here, asthey are similar to those described above.

As described in detail with reference to the first embodiment, thedevice 310 comprises a main body 312 with a substantially wedge-shapedopening 314 a and 314 b on respective side.

Two recesses or openings 318 are provided in the lower part of the mainbody 312. Two substantially cylindrical channels 319 are providedsubstantially vertically in the main body 312, from the lower part tothe upper part. Two, substantially T-shaped pressure elements 320 areprovided, each comprising a substantially vertical central member 350and a substantially horizontal cross member 352. The substantiallyvertical central member 350 comprises poles 322 provided through thesubstantially cylindrical channel 219. The substantially horizontalcross member 352 is connected to each pole 322. The tip of each crossmember 352 is pointing upwardly, forming an electrical contact 340.

Consequently, the substantially horizontal cross member 252 is providedfor pressing each wafer towards the upper surface of the substantiallywedge-shaped opening 214 a, 214 b in a direction parallel to thesubstantially vertical central member.

In this embodiment, both the substantially horizontal cross member 352and the substantially vertical central member 350 is electricallyconducting, forming the electrical connection to the power supply.

In their upper end, protruding out from each channel 319, the poles 322are provided with one common magnetic bus connector 344. The magneticbus connector 344 is provided for being attracted upwardly when theholding device is moving under a magnetic bus 348. The magnetic busconnector 344 and the magnetic bus 348 are also providing electricalcontact between the pressure element 320 and the power supply.

Consequently, when the holding device moves under the bus 348, thepressure elements 320 will be moved upwardly in a substantially linearmovement. Hence, when the pressure element is in this upper or closedposition, the holding device is both holding the wafer and at the sametime providing electrical contact to the wafer. When the pressureelement is in its lower or open position, the wafer may be received intoor released from the holding device.

FIFTH EMBODIMENT

In FIGS. 10 a and 10 b a fifth embodiment of the holding device isshown. This holding device is denoted with reference number 410. Manydetails regarding the fifth embodiment will not be described in detailhere, as they are similar to those described above.

As described in detail with reference to the first embodiment, thedevice 410 comprises a main body 412 with a substantially wedge-shapedopening 414 a and 414 b on respective side.

An opening 418 is provided in the main body 418. The opening 418 is acombination of the openings in the fourth embodiment and the opening ofthe second embodiment. The opening 418 comprises a longitudinal opening418 a provided in a longitudinal direction of the lower part of the mainbody, and two openings 418 b provided transverse to the longitudinalopening.

In this embodiment, the pressure elements 420 is similar to the pressureelements of the fourth embodiment, and will not be described here indetail. The pressure elements are provided in the transverse openings418 b of the main body. In addition, the pressure element 420 comprisesa buoyancy element 422 provided in the longitudinal opening 418 a. Thebuoyancy element 422 is fixed to the substantially vertical centralmember 450 or pole 422, and is vertically movable within the opening 418a. Hence, when the holding device is submerged in liquid, the buoyancyelement 422 will be pressed upwardly, and the pressure device will bepressed towards the wafer. When the holding device rises up from theliquid, the buoyancy element 422 will move downwardly, and the wafer maybe released from the holding device.

In this embodiment, both the substantially horizontal cross member 452and the substantially vertical central member 450 is electricallyconducting, forming the electrical connection to the power supply.

Hence, when the pressure element is in this upper or closed position,the holding device is both holding the wafer and at the same timeproviding electrical contact to the wafer. When the pressure element isin its lower or open position, the wafer may be received into orreleased from the holding device.

In the embodiments described above, the pressure element is movable inrelation to the main body. More specifically, the pressure element ismovable between an open position for receiving/releasing the wafer, anda closed position for holding and contacting the wafer. In the closedposition, the wafer is held between the main body and the pressureelement.

1. Transporting device for transporting wafers through a liquid, wherethe transportation device is provided for continuously receiving wafersat a first end and transporting them substantially horizontally to asecond end before releasing the wafers, where the transporting devicecomprises at least two holding devices for holding and electricallycontacting each wafer between the at least two contacting devices duringthe transportation through the liquid, where each holding devicecomprises: a main body comprising a substantially wedge-shaped openingfor receiving an end of each wafer; an electrical contact for contactingthe end of each wafer, where the electrical contact is connected to apower supply; a pressure element movably connected to the main body, forpressing the electrical contact towards the end of each wafer. 2.Transportation device according to claim 1, wherein the main bodycomprises one substantially wedge-shaped opening on each side. 3.Transportation device according to claim 1 or 2, where the electricalcontact is provided on the pressure element.
 4. Transportation deviceaccording to claim 1, where the pressure element is provided forpressing each wafer towards an upper surface of the substantiallywedge-shaped opening.
 5. Transportation device according to claim 4,where the pressure element is substantially T-shaped, comprising asubstantially vertical central member and a substantially horizontalcross member, where the substantially horizontal cross member isprovided for pressing each wafer towards the upper surface of thesubstantially wedge-shaped opening in a direction parallel to thesubstantially vertical central member.
 6. Transportation deviceaccording to claim 5, where the substantially vertical central member isprovided movable in a channel through the main body.
 7. Transportationdevice according to claim 4, where the pressure element is pivotablyconnected to the main body by means of a pin inserted in the opening ofthe main body.
 8. Transportation device according to claim 1, where theelectrical contact is connected to the power supply by means of a busconnector for connection to a bus bar.
 9. Transportation deviceaccording to claim 8, where the electrical contact is connected to thebus connector by means of an electrical conductor provided in channelsthrough the main body.
 10. Transportation device according to claim 3,where the electrical contact is upwardly protruding.
 11. Transportationdevice according to claim 1, where the pressure element is provided inan opening of the main body.
 12. Transportation device according toclaim 1, where the pressure element comprises floating elements forproviding the movement of the pressure element in relation to the mainbody due to buoyancy forces.
 13. Transportation device according toclaim 1, where the pressure element comprises a magnet for providing themovement of the pressure element in relation to the main body due tomagnetic forces.
 14. Device according to claim 1, where the pressureelement is connected to poles movably provided in channels in the mainbody.
 15. Device according to claim 14, where bus connectors having alarger diameter than the poles are connected in the end of the poles,and where the movement of the pressure element is caused by incliningbus bars guiding the bus connectors.
 16. Transportation device accordingto claim 2, where the pressure element is provided for pressing eachwafer towards an upper surface of the substantially wedge-shapedopening.
 17. Transportation device according to claim 3, where thepressure element is provided for pressing each wafer towards an uppersurface of the substantially wedge-shaped opening.